Well when it comes to retirement in football it something that has to do with person interest, imagine being in the system for over 15years, barely having time for your family, friends, kids and not being able to do some stuffs, all these are thing that trigger retirement in football. There are some who would even retire at their late 20s. So I would say it all individual differences when it comes to retirement in football.
You're right, but If you're actually into football for the passion, you most likely will want to retire base on age, except for the fact a case of critical health issues, because football is a career for most players and they're there for money and also for the entertainment so considering to quit football early due family not having much time with, means considering to resign your job when it's not yet time or when you haven't put a retirement plans in place, and talking about having time with your family, some of them move with their wifes and children, whereas some aren't married yet they only have their girlfriends.